At present, as a protocol for communication among computers (in the following description, computers and the like that perform communication/information processing may be generally referred to as “nodes”), the transmission control protocol/internet protocol (TCP/IP) is generally used. For communication using the TCP/IP, an IP address of a 32-bit configuration is assigned to each of the nodes.
This IP address includes a network section used for identifying a network to which each of the nodes belongs and a host section used for identifying each of the nodes in the network to which the node belongs.
The network section and the host section of the IP address are identified by a netmask of a 32-bit configuration. Each of the bits of the netmask is 1 when a bit of the IP address corresponding thereto is included in the network section and is 0 when the bit of the IP address is included in the host section (the number of bits being 1 is hereinafter referred to as the number of bits of the netmask).
As a protocol for managing the IP address and assigning the IP address to each of the nodes, the dynamic host configuration protocol (DHCP) is generally used.
Further, in recent years, there is a serious problem that programs (data) spread from computer to computer via a network and adversely effects on the computers in various ways to lead leakage of data from the computers and the like. Such programs (data) are also called computer viruses or worms.
A computer virus/worm is formed of a program code, a macro of a specific application program, and data for execution of the code and the macro, or a combination including one or more of the above. Hereinafter, the computer virus/worm is generally referred to as a computer virus or as a virus simply.
For example, Patent Document 1 discloses a method of preventing an illegal access to a DHCP server that provides a DHCP function in a network in which the IP address and the DHCP are used.
However, the method disclosed in Patent Document 1 cannot prevent an infection of a virus from spreading among computers connected to a network.
Patent Document 1: JP 2004-228799 A